Abstract:

An optical film, disposed in the backlight assembly, is provided. The
optical film is manufactured by the following method. First, curing glue
comprised of photocurable resin and thermosetting resin is provided.
Compared to the curing glue as a whole, the percentage weight of the
thermosetting resin is about 1%˜5%. Thereafter, the curing glue is
illuminated and heated in order to form the optical film.

Claims:

1. An optical film, disposed in the backlight assembly, fabricated by a
process comprising:mixing a photocurable resin and a thermosetting resin
to form a curing glue, wherein a percentage weight of the thermosetting
resin is about 1%˜5% of the weight of the curing glue as a
whole;illuminating and heating the curing glue to cure the curing glue;
andforming the optical film, wherein a plurality of first microstructures
is disposed on the optical film.

2. The optical film of claim 1, wherein the photocurable resin is an UV
curing resin.

3. The optical film of claim 1, wherein the first microstructures,
comprising of the shape of a prism, are disposed on an emergent surface
of the optical film.

4. The optical film of claim 1, wherein the first microstructures,
comprising of a hemi-spherical shape, are disposed on the emergent
surface of the optical film.

5. The optical film of claim 1, wherein the thickness of the optical film
is above 30 μm.

6. The optical film of claim 1, wherein the thermosetting resin is
selected from the group consisting of polyester and polyurethane.

7. A manufacturing method of optical film, comprising:coating an uncured
curing glue on a forming mold, wherein a plurality of second
microstructures is disposed on the forming mold, the curing glue is
coated on the second microstructures, the curing glue is made by mixing
together the photocurable resin and the thermosetting resin, and the
percentage weight of the thermosetting resin is about 1%˜5%
compared to the weight of the curing glue as a whole;covering a pressing
plate on the curing glue, wherein a release film is disposed between the
pressing plate and the forming mold;illuminating and heating the curing
glue to cure the curing glue;separating the cured curing glue from the
pressing plate and the forming mold;cutting the cured curing glue to form
a plurality of optical film; anddetaching the release film from the
optical film.

8. The manufacturing method of the optical film of claim 7, wherein the
photocurable resin is an UV curing resin.

9. The manufacturing method of the optical film of claim 7, wherein the
viscosity of the photocurable resin is above 250 cps.

10. The manufacturing method of the optical film of claim 9, wherein the
viscosity of the photocurable resin is between 250 cps and 600 cps.

11. The manufacturing method of the optical film of claim 7, wherein the
thermosetting resin is selected from the group consisting of polyester
and polyurethane.

12. The manufacturing method of the optical film of claim 7, wherein a
release agent is coated on the surface of the forming mold.

Description:

FIELD OF INVENTION

[0001]The present invention relates to an optical film, especially relates
to an optical film disposed in the backlight assembly.

BACKGROUND OF THE INVENTION

[0002]In recent years, the traditional Cathode Ray Tube display,
hereinafter referred to as CRT display, is gradually replaced by the
liquid crystal display, hereinafter referred to as LCD display. The major
reason for this trend is because that the radiation emitting from the LCD
display is far less than the CRT display, and that the cost of the LCD
display is significantly reduced. In general, the LCD display includes a
backlight assembly and a LCD panel. The principal function of the
backlight assembly is used as the light source for the LCD display.

[0003]In general, the backlight assembly includes a plurality of cold
cathode fluorescent lamps, a reflective housing, a diffusion plate, a
diffusion film, and a brightness enhancement film. The cold cathode
fluorescent lamps are used to generate the light. The reflective housing
is used to reflect the light from the cold cathode fluorescent lamps to
the diffusion plate. The diffusion plate is used to diffuse the light
from the cold cathode fluorescent lamps, in order to ensure further light
illumination uniformity to the LCD panel, so as to reduce the non-uniform
brightness phenomenon at the display surface of the LCD display. Because
a plurality of diffusion particles are disposed in the diffusion plate,
therefore, the transmittance of the diffusion plate is thereby decreased.
Generally speaking, the transmittance of the diffusion plate is between
50% to 70%.

[0004]However, typically the use of the diffusion plate is not enough to
overcome the non-uniform brightness phenomenon. Therefore, a diffusion
film is needed to further diffuse the light. The diffusion film is an
optical film having a plurality of diffusion particles thereon. In order
to enhance the brightness throughout the entire viewing angle range, the
brightness enhancement film is thereby added on the diffusion film.

[0005]Please refer to FIG. 1. FIG. 1 is a front view of a conventional
brightness enhancement film 110. The brightness enhancement film 110 is
comprised of a base plate 111 and a structured layer 112. The thickness
of the base plate 111 is about 175 μm. The material of the base plate
111 is transparent polyethylene terephthalate, hereinafter referred to as
PET. Furthermore, adhesives are coated on the base plate 111. The
thickness of the structured layer 112 is about 25 μm. The material of
the structured layer 112 is photosensitive acrylic resin. The structured
layer 112 is combined and joined with the base plate 111 by using the
adhesives. Due to the prismatic microstructures on the structured layer
112, the brightness enhancement film 110 is able to condense the light.
Consequently, the angle for the emergent light from the brightness
enhancement film 110 will become narrowed, so as to increase the
brightness within the viewing angle range.

[0006]However, the usage of the base plate 111 will increase the overall
material cost. Furthermore, based on the consideration of the optical
quality, the base plate 111 must have higher transmittance, generally
above 89%. Hence, the material cost will be further increased.

[0007]Moreover, some amount of light can be absorbed by the base plate 111
and the structured layer 112. Consequently, after entering into an
incident surface 113 of the brightness enhancement film 110, the incident
light L1 needs to pass through two mediums, i.e. the base plate 111 and
the structured layer 112, before emitting from an emergent surface 114 of
the brightness enhancement film 110. Therefore, the loss of light will be
increased.

[0008]Hence, there is a need in the art for decreasing the material costs
of the brightness enhancement film 110 and the loss of light.

SUMMARY OF THE INVENTION

[0009]One object of the present invention is to provide an optical film
and manufacturing method thereof. The optical film has lower material
cost and can reduce the loss of light.

[0010]To achieve the foregoing and other object, an optical film is
disclosed. The optical film used in the backlight assembly is mainly made
by the following process. In the first step, a photocurable resin and a
thermosetting resin are mixed together to form a curing glue. Compared to
the curing glue as a whole, the percentage weight of the thermosetting
resin is about 1%˜5%. In the second step, the curing glue is
illuminated by light and heated to be cured to become a cured sample. In
the third step, the optical film is formed, for example by cutting the
cured sample into individual sheets. A plurality of first microstructures
is disposed on the optical film.

[0011]In the optical film, the photocurable resin is an UV curing resin.

[0012]In the optical film, the first microstructures are disposed on the
emergent surface of the optical film. The shape of the first
microstructures is that of a prism or a hemi-sphere.

[0013]In order to achieve the predetermined mechanical strength, the
thickness of the optical film is above 30 μm.

[0014]In the optical film, the thermosetting resin is selected from the
group consisting of polyester and polyurethane.

[0015]To achieve the foregoing and other object, a manufacturing method of
optical film is provided. The manufacturing method includes the following
steps:

[0016]In the first step, an uncured curing glue is coated on a forming
mold. A plurality of second microstructures is disposed on the forming
mold. The curing glue, which is made by mixing the photocurable resin and
the thermosetting resin, is coated on the second microstructures. The
percentage weight of the thermosetting resin is about 1%˜5%
compared to the weight of the curing glue as a whole.

[0017]In the second step, a pressing plate is covered on the curing glue.
A release film is disposed between the pressing plate and the forming
mold.

[0018]In the third step, the curing glue is illuminated by light, and is
heated to be cured to become a cured sample.

[0019]In the fourth step, the cured sample is separated from the pressing
plate and the forming mold.

[0020]In the fifth step, the cured sample is cut into individual sheets to
form a plurality of optical film.

[0021]In the sixth step, the release film is separated from the optical
film.

[0022]In the manufacturing method of the optical film, the photocurable
resin is an UV curing resin.

[0023]In the manufacturing method of the optical film, the photocurable
resin is an UV curing resin.

[0024]In the manufacturing method of the optical film, the viscosity of
the photocurable resin is above 250 cps. Furthermore, the viscosity for
the photocurable resin between 250 cps and 600 cps is preferred.

[0025]The above and other aspects, features, and advantages of the present
invention will become more apparent from the following detailed
description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a front view of a conventional brightness enhancement
film.

[0027]FIG. 2A to FIG. 2D shows a manufacturing process of an optical film
according to an embodiment of the present invention.

[0028]FIG. 3 shows the brightness enhancement film in the embodiment of
the present invention.

[0029]FIG. 4 shows the forming mold for manufacturing the optical film
with diffusion capability.

[0030]FIG. 5 shows the diffusion film in the embodiment of the present
invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031]Referring to FIG. 2A to FIG. 2D, FIG. 2A to FIG. 2D shows the
manufacturing process of the optical film in an embodiment of the present
invention. Referring to FIG. 2A, a forming mold 40 is provided. A
plurality of second microstructures 42 is disposed on a surface 41 of the
forming mold 40. The second microstructures 42 are in the shape of
prismatic trough. The material of the forming mold 40 is made of metal,
for example, nickel and copper. Otherwise, the release agent, can be made
of, for example, Teflon and is coated on the surface 41 of the forming
mold 40.

[0032]Referring to FIG. 2B, a curing glue 20 is coated on the surface 41
of the forming mold 40. The viscosity of the curing glue 20 is above 250
cps, and the preferred viscosity of the curing glue 20 is between 250 cps
and 600 cps. The curing glue 20 is made by mixing together the
photocurable resin and the thermosetting resin. Compared to the curing
glue 20 as a whole, the percentage weight of the thermosetting resin is
about 1%˜5%. Herein, the photocurable resin is cured when it is
illuminated by light at a specified range of wavelengths band. In this
embodiment, the photocurable resin is an UV curable resin, which is cured
after being illuminated by ultraviolet radiation.

[0033]The UV curable resin is widely used because of its beneficial
characteristics, such as for example, higher toughness, easy to forming,
and convenient to processing. The UV curable resin is mainly comprised of
oligomers, for example, polyester acrylic oligomer, epoxy acrylic
oligomer, or polyurethane acrylic oligomer. Furthermore, a reactive
monomer and a photo initiator can be added into the UV curable resin, in
order to improve the performance characteristics and reaction rate of the
UV curable resin. The thermosetting resin is made for example of
polyester or polyurethane.

[0034]Referring to FIG. 2c, a pressing plate 50 is covered on the curing
glue 20. The pressing plate 50 is made of a transparent material. A
release film 80 is disposed between the pressing plate 50 and the curing
glue 20. The release film 80 is made of a transparent material, for
example, polyethylene terephthalate, oriented polypropylene or other
transparent material that would not crosslink with the curing glue 20.
Furthermore, a small amount of additives is coated on the release film
80, to allow the release film 80 to be adhered on the curing glue 20.

[0035]Referring to FIG. 2D, a light source 60 is used to illuminate the
curing glue 20. During the meantime, a heat pipe 70 is used to heat the
curing glue 20. Because the pressing plate 40 is made of a transparent
material, the light from the light source 50 can pass through the
pressing plate 40 and the release film 80, and then to illuminate on the
curing glue 20. Thereafter, the photocurable resin inside the curing glue
20 would undergo chemical reactions and begin to be cured. Furthermore,
the thermosetting resin would undergo more reactions and begin to be
cured by absorbing the heat from the heat pipe 70. In the embodiment, the
light source 60 is a ultraviolet light source. In addition, the heat pipe
70 can be replaced by other heating devices. For example, the curing glue
can be baked by hot wind.

[0036]After a specified period of time, the curing glue 20 will become
completely cured. Because the release film 80 is located between the
curing glue 20 and the pressing plate 50, the pressing plate 50 can be
removed. In this embodiment, Teflon is coated onto the forming mold 40,
so the curing glue 20 can be easily removed from the forming mold 40.
Afterwards the curing glue 20 is cut into a plurality of brightness
enhancement films 210 (as shown in FIG. 3). The brightness enhancement
film 210 has a plurality of first microstructures 211. At this moment,
the release film 410 is still adhered on the bottom side of the
brightness enhancement film 210. Because the release film 80 is adhered
on the brightness enhancement film 210 by means of only a small amount of
additives, the release film 80 can be easily detached or removed. In view
of preventing from environmental contamination during shipment and
storage, the release film 80 is not removed until when the brightness
enhancement film 210 is ready to be used. Moreover, in order to protect
the first microstructures, a protective film can be adhered on the top
surface of the brightness enhancement film 210.

[0037]Compared to the brightness enhancement film 110 in FIG. 1, the
brightness enhancement film 210 according to the present embodiment of
the present invention has no base plate, therefore the material cost and
thickness can be reduced. In this embodiment, the thickness of the
brightness enhancement film 210 is preferably maintained above 30 μm,
in order to ensure the brightness enhancement film 210 to be able to
maintain at a predetermined acceptable level of mechanical strength.
Herein, the thickness of the brightness enhancement film 210 is defined
to be the distance from the incident surface 212 to the peak of the first
microstructures 211. After entering into the incident surface 213 of the
brightness enhancement film 210, the light L2 passes through only one
layer of medium. Hence, as compared to the brightness enhancement film
110, the loss of light would be decreased. Furthermore, design variables
which the designer must consider would be reduced, so that the degree of
difficulty relating to design will be lowered.

[0038]From above, those skilled in the art would appreciate that the
brightness enhancement film 210 come to have better properties and lower
cost.

[0039]In general, as the second microstructures 42 are more densely
distributed, it becomes more difficult to detach the curing glue 20 away
from the forming mold 40. Therefore, it is better to coat the release
agent on the surface 41 of the forming mold 40, so that the curing glue
which has been cured can then be more easily detached or taken away from
the forming mold 40. If the distribution of the second microstructures 42
is less populated and looser, it is then not necessary to coat the
release agent onto the surface 41 of the forming mold 40.

[0040]By means of the manufacturing process shown in FIG. 2A to FIG. 2D,
not only the brightness enhancement film 210 but also the optical film
with diffusion capability can be produced. Referring to FIG. 4, FIG. 4
shows the forming mold 40' used for manufacturing the optical film with
diffusion capability. One difference between the forming mold 40' and the
forming mold 40 (shown in FIG. 2A) is that the second microstructures 42'
on the forming mold 40' is in the shape of a semi-spherical trough. By
coating the curing glue 20 (shown in FIG. 2B) on the forming mold 40' and
undergoing the process shown in FIG. 2c and FIG. 2D, the diffusion film
210' shown in FIG. 5 shall be produced. The thickness of the diffusion
film 210' is between 0.1 mm and 0.2 mm according to the present
embodiment. Because of its hemi-spherical shape, the light will be
diffused by the first microstructures 211'. In FIG. 5, the first
microstructures 211' are arranged at equal intervals, but those skilled
in the art can easily arrange the first microstructures 211' in a random
formation.

[0041]If the curing glue is to be totally comprised of the photocurable
resin (hereinafter the curing glue is referred to as the second curing
glue), the optical film can be easily deformed and broken apart. The
reason for this is herein described in detail. When the second curing
glue which is totally comprised of photocurable resin is illuminated by
light, the outer portion of the second curing glue will be cured earlier
than the inner portion thereof. If the illuminating duration for the
second curing glue is equal to that for the curing glue 20 shown in FIG.
2D, some uncured curing glue would be remaining inside the optical film
(hereinafter referred to as the second optical film) made from the second
curing glue. Or, a longer illuminating duration is required to permit the
second curing glue to be totally cured, however, this will lead to
reduced production rate.

[0042]After performing a temperature cycling test, the shrinkage rate of
the second optical film would be larger than that of the brightness
enhancement film 210. Said this temperature cycling test is typically
used to assess whether the optical film is able to perform properly under
harsh operating conditions and environments. If the test is passed, the
optical film shall have longer service life.

[0043]During the temperature cycling test, the set temperature in the test
environment is raised and maintained at a higher temperature (for
example: 85° C.) for a period of time (for example: 1 hour). Then
the set temperature in the test environment is decreased and maintained
at a lower temperature (for example: -35° C.) for a period of time
(for example: 1 hour). Thereafter, the above cycle is repeated for
4˜5 days. It is found that the second optical film shrank 2%, but
the brightness enhancement film 210 only shrank 0.31%. From the above,
those skilled in the art should know the brightness enhancement film 210
would be better able to withstand the temperature variations of the
external environment.

[0044]Because there is uncured second curing glue left in the interior of
the second optical film, the outer portion and the inner portion of the
second optical film will undergo different deformation. Hence some cracks
will be generated on the surface of the second optical film, the uncured
second curing glue located in the interior of the second optical film
will be dissipated from the cracks, and then the second optical film will
be shrunk.

[0045]The brightness enhancement film 210 manufactured from the curing
glue 20 is mainly comprised of the photocurable resin and the
thermosetting resin. After being heated, the thermosetting resin will
release free radicals. The free radicals will further chemically react
with the photocurable resin, so as to allow the uncured curing glue to be
cured. Therefore, the uncured curing glue is thus made to be more
difficult to be left inside the brightness enhancement film 210, and
thereby the yield rate will be increased.

[0046]If the percentage weight of the thermosetting resin is less than 1%,
more uncured curing glue will be left inside the brightness enhancement
film 210. If the percentage weight of the thermosetting resin is more
than 1%, the brightness enhancement film 210 will become brittle.
Therefore, the percentage weight of the thermosetting resin is about
1%˜5% when compared to the weight of the curing glue 20 in this
embodiment.

[0047]Although the description above contains many specifics, these are
merely provided to illustrate the invention and should not be construed
as limitations of the invention's scope. Thus it will be apparent to
those skilled, in the art that various modifications and variations can
be made in the system and processes of the present invention without
departing from the spirit or scope of the invention.